The present invention relates to a control system for docking a marine vessel.
Today's marine vessels are often equipped with a plurality of propulsion units, for example three, for driving the vessel. If every propulsion unit is associated to a separate control lever the handling of the vessel can be unnecessarily complicated. As many users of marine vessels are not experienced helmspersons, a simplified control system is desirable.
WO 2007/105995 describes a control system for a set of propulsion units where a centrally arranged propulsion unit of the set is controlled as a slave based on control signals provided by at least one of the remaining propulsion units of the set. Thereby, the number of control levers are decreased, for example from three to two, thus the control system for the vessel is simplified.
However, there is always a desire to even further simplify the handling of a marine vessel, for example by means of introducing further improvements to the control system for controlling a set of marine propulsion units.
It is desirable to achieve a control system for a set of marine propulsion units and a marine vessel with such a control system that is further simplified.
The inventor has realized that the thrust that can be applied from each propulsion unit is limited due to the propeller cavitation effect, resulting in reduction of the total thrust generated on the vessel. The invention is based on the inventor's realization that the cavitation typically occurs on the propulsion unit with reverse gear engaged, and that in a triple propulsion unit installation the normally idle center propulsion unit can be used to increase the reverse thrust and thereby limit the RPM of propulsion units in reverse, so that the cavitation effect is limited, and simultaneously allow for higher forward thrust on the third propulsion unit, thus increasing the total thrust for the vessel.
According to a first aspect of the inventive concept, a marine propulsion control system for controlling a set of propulsion units carried by a hull of a vessel, wherein the set of propulsion units comprise a first propulsion unit, a second propulsion unit and a third propulsion unit, wherein the second propulsion unit is provided as a center propulsion unit between the first and third propulsion unit, the marine propulsion control system comprising a control unit configured to receive an input command from a steering control instrument for operating the vessel, determine a desired delivered thrust, gear selection and steering angle for the first, second and third propulsion unit respectively, based on the input command, and provide a set of control commands for controlling the desired delivered thrust, gear selection and steering angle for the first, second and third propulsion unit, wherein if the input command indicates a sway command the first propulsion unit is set to have a forward gear selection and the third propulsion unit is set to have a reverse gear selection, each with a selected thrust level, and if the thrust level for at least one of the first and the third propulsion unit exceeds a predetermined thrust level the second propulsion unit is set to have a reverse gear selection with a thrust level depending on the selected thrust level of at least one of the first and the third propulsion unit.
In the context of this application a vessel should interpreted as any type of vessel, such as larger commercial ships, smaller vessel such as leisure boats and other types of water vehicles or vessels.
Furthermore, in the context of this application “gear selection” should be interpreted as selection of rotation direction of the propeller, i.e. forwards or rearwards rotation direction.
Through the system described, the propulsion units can be controlled individually. Thereby the propulsion units may for example be switched independently between a forward propulsion state and a reverse propulsion state and steered independently of one another.
By allowing the second propulsion unit to assist the first or third propulsion unit in creating a reverse thrust on the vessel, the total thrust of the vessel can be increased with 80-100 percent. Thereby, an operator of the vessel has more thrust to control the vessel, thus allowing the operator to act later and with more effect which means facilitated handling of the vessel.
Many inexperienced operators compare operating a marine vessel to operating a land vehicle, e.g. a car, and one of the hardest things to learn is how the marine vessel drifts due to inertial effects, wind and currents, which require the operators to plan their movements long in advance. When increased thrust to control the vessel is provided, the operator can reduce the time-span of the vessel's planned movements. This is a great advantage for an inexperienced operator.
In one embodiment the steering angle of the second propulsion unit is substantially the same as the steering angle of the third propulsion unit.
The first propulsion unit can be either a starboard or a port propulsion unit. Consequently, the third propulsion unit can be either a port or a starboard propulsion unit. The vessel will sway in the same direction as the position of the propulsion unit that is set with a reverse gear selection relative a thought center line. Thus, if the first propulsion unit is a port propulsion unit and the first propulsion unit is set in a reverse gear selection, the vessel will sway in a port direction.
Preferably, the first and third propulsion units' steering angles are substantially inverted relative a longitudinal axis. In the context of this application a longitudinal axis should be interpreted as an axis extending from the vessel's bow to the vessel's stern.
In one embodiment of the invention the first and third propulsion unit angles are set to an outwards angle. Thereby a component force in the lateral axis achieving a sway movement of the vessel is provided.
In another embodiment the first and third propulsion unit angles are set to a substantially maximum outwards angle. Thereby, the component force in the lateral axis achieving a sway movement of the vessel may be substantially maximized.
Further, if the first and third propulsion units are substantially inverted relative the longitudinal axis, and their thrust level are substantially equal, the force component in a forward/reverse direction will be zero, thus only a sway movement of the vessel will be achieved.
According to another embodiment, the marine propulsion control system further comprises three independent Engine Control Unit for providing an interface between the control unit and the first, second and third propulsion unit respectively. Thereby, the control unit does not have to comprise an interface for communicating with each of the first, second and third propulsion unit. Moreover, existing ECUs in a marine vessel can be utilized. According to yet another embodiment of the inventive concept, the three independent ECUs are electrically connected to the control unit.
According to another embodiment, the predefined level of the thrust level for one of the first or third propulsion unit corresponds to a level less than where a reverse propulsion direction of the first or third propulsion unit causes cavitation. Thereby, the cavitation effect typically occurring in the propulsion unit with a reverse gear selection can be alleviated through that the second propulsion unit assists the propulsion unit with a reverse gear selection by also creating a reversely directed thrust. By avoiding cavitation effects the total thrust of the vessel can be increased further.
According to yet another embodiment, the marine propulsion control system further comprises a steering control instrument for providing the control unit with an input command. Thereby, the operator can easily provide input commands to the control unit, so that the control unit can control the propulsion units in a direction desired by the operator.
Preferably, the inventive control system forms part of a marine vessel, further comprising a first propulsion unit, a second propulsion unit, a third propulsion unit, wherein the second propulsion unit is provided as a center propulsion unit between the first and second propulsion unit, each propulsion unit are carried by a hull.
By providing a vessel with a marine propulsion control system allowing the second propulsion unit to assist the first or third propulsion unit in creating a reverse thrust on the vessel, the total thrust of the vessel can be increased. Thereby, an operator of the vessel has more thrust to control the vessel, thus allowing the operator to act later and with more effect which implies facilitated handling of the vessel.
According to a second aspect of the present inventive concept, there is provided a method for controlling a set of propulsion units carried by a hull of a vessel, wherein the set of propulsion units comprise a first propulsion unit, a second propulsion unit and a third propulsion unit, wherein the second propulsion unit is provided as a center propulsion unit between the first and second propulsion unit, the method comprising receiving an input command from a steering control instrument operating the vessel, determining a desired delivered thrust, gear selection and steering angle for the first, second and third propulsion unit respectively, based on the input command, and providing a set of control commands for controlling the desired delivered thrust, gear selection and steering angle for the first, second and third propulsion unit, and setting the second propulsion unit to have a reverse gear selection with a thrust level if the input command indicates a sway command and the first propulsion unit is set to have a forward gear selection and the third propulsion unit is set to have a reverse gear selection, each with a thrust level, and if the thrust level for one of the first or the third propulsion unit exceeds a predetermined thrust level.
The effects of a method as described above are largely analogous to the effects of a marine propulsion control system and a vessel as described above. By providing a method for allowing the second propulsion unit to assist the first or third propulsion unit in creating a reverse thrust on the vessel, the total thrust of the vessel can be increased substantially. Thereby, an operator of the vessel has more thrust to control the vessel, thus allowing the operator to act later and with more effect which implies facilitated handling of the vessel.
According to another embodiment, the method further comprises providing the predefined thrust level for one of the first or the third propulsion unit so that it corresponds to a level less than where a reverse propulsion direction of the first or third propulsion unit causes cavitation. Thereby, the cavitation effect typically occurring in the propulsion unit with a reverse gear selection can be alleviated through that the second propulsion unit assists the propulsion unit with a reverse gear selection by also creating a reversely directed thrust. By avoiding cavitation effects the total thrust of the vessel can be increased further, which in turn means facilitated handling.
According to a third aspect of the present invention there is provided a computer program product comprising a computer readable medium having stored thereon computer program means for causing a control unit to control a set of propulsion units carried by a hull of a vessel, wherein said set of propulsion units comprise a first propulsion unit, a second propulsion unit and a third propulsion unit, wherein said second propulsion unit is provided as a center propulsion unit between said first and second propulsion unit, wherein the computer program product comprises code for receiving an input command from a steering control instrument operating the vessel, code for determining a desired delivered thrust, gear selection and steering angle for said first, second and third propulsion unit respectively, based on the input command, code for providing a set of control commands for controlling the desired delivered thrust, gear selection and steering angle for said first, second and third propulsion unit, and code for setting said second propulsion unit to have a reverse gear selection with a thrust level if said input command indicates a sway command and the first propulsion unit is set to have a forward gear selection and the third propulsion unit is set to have a reverse gear selection, each with a thrust level, and if the thrust level for one of said first or said third propulsion unit exceeds a predetermined thrust level.
The control unit is preferably a micro processor or similar device, and the computer readable medium may be one of a removable nonvolatile random access memory, a hard disk drive, a floppy disk, a CD-ROM, a DVD-ROM, a USB memory, an SD memory card, or a similar computer readable medium known in the art. The effects of a the computer product implementation of the invention for controlling a set of propulsion units by a control unit as described above are largely analogous to the effects of a marine propulsion control system, vessel and method as described above.
Furthermore, a code for controlling a set of marine propulsion units allows a user to upgrade an existing marine propulsion control system that allows separate individual control of the steering angle, thrust level and gear selection of the set or propulsion units. With abovementioned code, the upgrade could be done carried out with merely software alterations, vastly reducing the costs for a vessel owner to upgrade the marine propulsion control system.